Replacing throttle body gasket

Tiny
POORPONTIAC
  • MEMBER
  • 2003 PONTIAC BONNEVILLE
  • 3.8L
  • V6
  • FWD
  • AUTOMATIC
  • 175,000 MILES
I was replacing my throttle body gasket because I had no vacuum leak from the old gasket. One, while putting the bolts back on for the throttle body the stud for one snapped. How do I remove the stud without messing up my intake manifold or having to re drill everything? It has a plate on the back of the stud, but it is very thin. Two, when the bolts are tight should I be able to seethe side of my gasket in a small gap on one side? Is it still sealed?
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Sunday, April 16th, 2017 AT 12:09 AM

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Tiny
CARADIODOC
  • EXPERT
I had a broken bolt exactly like yours on my 1988 Grand Caravan a few years ago, but it was for the thermostat housing. It created the perfect "teachable moment" for my students and especially the kid who felt bad for breaking it. You will need a wire feed welder and an acetylene torch. Propane torch will not work. The flame is too large and not hot enough. Grab a nut with a center hole slightly larger than the bolt diameter. Center the nut over the broken bolt. Use a small torch tip with a nice blue flame with a sharp point. The tip of the flame is the hottest part of the flame. Touch that tip to the center of the bolt to warm it up. The goal is to get the bolt red hot but it never will get that hot because the heat is being sucked away by the intake manifold. Nevertheless, heat the bolt for at least a couple of minutes. Stay away from the nut as much as possible. You want it to stay cool. If you are careful and quick, you can heat the bolt first, then set the nut in place with a pliers just when you are ready to weld. When the bolt is as hot as it's going to get, hand the torch off to a helper and immediately grab the welder. Feed the wire onto the end of the bolt and start to build it up. Stay away from the nut as long as possible. Do not stop welding because you do not want the bolt to have a chance to cool down. As the weld builds, it will fill the hole in the nut and eventually you will also be welding to the nut. The nut will turn orange. That is okay, but stop welding before the sides of the nut start to melt. You need those sides to be in good shape so a socket will fit on the nut.

Welding works, not by "sticking" to the metal, but by melting the surfaces of the two pieces of metal with a filler metal in between. That's called "penetration". If you do not preheat the bolt, the heat from the welder will be sucked away before the metal of the bolt melts. You will end up building up the weld until it melts to the nut but it will not have penetrated the bolt. That would be like putting glue on the piece of wood you are using to build a bird house, then assembling the pieces after the glue dries. The preheating gets the bolt up to its melting temperature sooner. It has to reach that temperature from welding before the weld builds up to the nut.

Once the nut is welded to the bolt, let it cool by itself for, oh, about ten seconds, then dribble a little water on the nut. Do not pour so much that it floods the surrounding area. You want to shrink the bolt but leave the intake manifold hot. The shock from the water will help break the bond between the bolt and intake manifold. Use a six point socket, ratchet, and extension on the nut to turn the bolt out. If the weld did not stick to the bolt and you twist the nut off, just grab another nut and try again. I have already had to resort to as many as six attempts before this worked. Sometimes this works better with two people, one to run the torch and one to be standing ready with the welder. Use a high setting on the welder to insure good penetration into the bolt before the weld builds up to the nut.

If that does not work, you can also drill through the center of the bolt, then use an "easy out" to try to unscrew the bolt. If you end up damaging the threads, you can install a Heli-Coil insert. If you have never done one or seen one, the people at any auto parts store can show you what to do.

Once the tap has gone in a few turns, back it off a quarter turn to break off any chips, then go another quarter to half turn. Keep doing this until you feel the resistance suddenly increase a lot. That means you are butting up against the chips that fell to the bottom of the hole. Unscrew the tap and clean the chips out again, then run the tap down once more. You will feel the tap get tight just like a bolt gets tight. Do not force it. I cannot remember if your intake manifold is made from aluminum or cast iron. If it is aluminum, it will tap very easily, but it will be easy to peel the new threads off too if you force the tap once it becomes tight. Blow the chips out again so the bolt will not butt up against them.

So, blow the metal chips out after drilling so the tap will go in all the way, and blow them out again after tapping so the bolt can go in all the way. The insert is a wound-up stainless steel spring. The outer part forms threads that match the threads you just cut. The inner part forms threads that match the new bolt. There is a plastic tool in the kit that threads onto the insert, then you use that to wind the insert into the hole. The insert will shrink as you wind it in since it is just a spring. You will be able to do that with just two fingers. There are two important things to watch for. First, you must wind it all the way in so no part of it sticks up above the surface of the intake manifold. If it sticks up, the thermostat housing, (throttle body), will sit on top of it and be held up. There is a chance the gasket will not be thick enough to seal the gap. If you cannot get it to screw in far enough, either the hole must be drilled deeper or you can try again with a second insert. Use an air cutoff tool to cut off one or two coils at the top of the insert. What is left will be plenty sufficient to do the job. To remove the first insert, grab the end of the coil with a needle nose pliers and twist it counter-clockwise. If it refuses to unscrew, which sometimes happens, twist and tug on it at the same time to uncoil it.

You can also use a cutoff tool to carefully grind down any part of the insert that is exposed above the surface of the intake manifold.

If you do try to drill the bolt out, the most important step is to grind the end flat, then punch a center mark to prevent the drill bit from wandering off to the side. Life will be much easier if you can keep the drill bit centered and straight. Drill the hole progressively bigger, but only until you just about reach the threads. If the "easy out" grabs the threads in the hole, it will be trying to peel those threads rather than trying to rotate the stud.

As far as seeing the sides of the gasket, that depends on the design of the parts. It is typical to see the gasket under most throttle bodies. The issue is whether it seals properly.
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Sunday, April 16th, 2017 AT 12:40 AM

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